Submission #427230

#	Time	Username	Problem	Language	Result	Execution time	Memory
427230		keko37	The Xana coup (BOI21_xanadu)	C++14	100 / 100	149 ms	24340 KiB

xanadu

#include<bits/stdc++.h>

using namespace std;

typedef long long llint;
typedef pair <int, int> pi;

const int MAXN = 100005;

int n;
llint dp[MAXN][2][2], par[MAXN], col[MAXN];
vector <int> v[MAXN];

void dfs (int x, int rod) {
    par[x] = rod;
    for (auto sus : v[x]) {
        if (sus != rod) dfs(sus, x);
    }
}

llint calc (int x, int f, int p) {
    if (dp[x][f][p] != -1) return dp[x][f][p];
    llint res = 1e9;
    llint sum = 0, br = 0, mn = 1e9;
    for (auto sus : v[x]) {
        if (sus == par[x]) continue;
        llint a = calc(sus, 0, f);
        llint b = calc(sus, 1, f);
        sum += min(a, b);
        if (b <= a) br ^= 1;
        mn = min(mn, abs(a - b));
    }
    if (br != f ^ p ^ col[x]) res = sum + mn; else res = sum;
    res += f;
    return dp[x][f][p] = res;
}

int main () {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    memset(dp, -1, sizeof dp);
    cin >> n;
    for (int i = 0; i < n-1; i++) {
        int a, b;
        cin >> a >> b;
        v[a].push_back(b);
        v[b].push_back(a);
    }
    for (int i = 1; i <= n; i++) {
        cin >> col[i];
    }
    dfs(1, 0);
    llint sol = min(calc(1, 0, 0), calc(1, 1, 0));
    if (sol >= 1e9) cout << "impossible"; else cout << sol;
    return 0;
}

Compilation message (stderr)

xanadu.cpp: In function 'llint calc(int, int, int)':
xanadu.cpp:33:12: warning: suggest parentheses around comparison in operand of '^' [-Wparentheses]
   33 |     if (br != f ^ p ^ col[x]) res = sum + mn; else res = sum;
      |         ~~~^~~~

• Subtask 1: 5 / 5
• Subtask 2: 15 / 15
• Subtask 3: 10 / 10
• Subtask 4: 40 / 40
• Subtask 5: 30 / 30